Method of making semiconductor device

ABSTRACT

In formation of a DRAM, a silicon nitride film is used as a mask to simultaneously expose a semiconductor substrate serving as an active region where an MOSFET is formed and a portion of the periphery of a trench. Therefore, even if the alignment offset of a resist pattern occurs, an interval between adjacent memory cells does not change. The interval between the adjacent memory cells is constantly the same as that when no alignment offset of the resist patter occurs. That is, only an n-type diffusion layer of the memory cell formed at a position adjacent to the trench comes close to source and drain regions of the adjacent memory cell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of making a semiconductordevice and, more particularly, to a method of making a DRAM.

2. Description of the Related Art

A conventional method of making a DRAM will be described by exemplifyinga semiconductor device disclosed in Jpn. Pat. Appln. KOKAI PublicationNo. 3-69185 (to be referred to as a reference hereinafter). FIG. 6A is aview showing part of the drawing in this reference. FIG. 6B is a viewshowing the semiconductor device in FIG. 6A when viewed from the top.

FIG. 6A shows the capacitor portion of a DRAM. A silicon oxide film 101and a silicon nitride film 102 are formed over a semiconductor substrate100. After patterning the silicon oxide film 101 and the silicon nitridefilm 102, the silicon nitride film 102 is used as a mask to form atrench 103 in the semiconductor substrate 100.

A capacitive insulating film 104 is formed in the inner wall and thebottom surface of the trench 103. The trench 103 is then filled with apolysilicon film 105. A resist film 106 having an etching resistanceagainst the polysilicon film 105 is formed over the entire surface. Theresist film 106 is lithographed and developed to form an opening 107 ina portion of the periphery of the trench 103. The resist film 106 havingthe opening 107 is used as a mask to etch part of the polysilicon film105, thereby forming a connect region 109 (shown in FIG. 6B).

However, the following problem is posed in the above method. That is,for example, as shown in FIG. 6B, the interval between adjacent memorycells is set to a predetermined distance w. As shown in FIG. 7, if thealignment offset of the resist pattern occurs when the resist film 106is lithographed and developed to form the opening 107 in the portion ofthe periphery of the trench 103, the alignment offset of a connectregion 109', the interval between the source and drain regions 108 ofthe adjacent memory cells is set to W' smaller than the predeterminedinterval w between the adjacent memory cells. For this reason,punch-through occurs between the adjacent memory cells.

Summary of the Invention

It is an object to provide a method of making a semiconductor device, inwhich even if the alignment offset of a resist pattern occurs when anopening is formed in a portion of the periphery of a trench, nopunch-through occurs between adjacent memory cells.

According to one aspect of the present invention, there is provided amethod of making a semiconductor memory device, which includes:preparing a semiconductor substrate of a first conductivity type,forming a first insulating film over the semiconductor substrate,forming a trench in the semiconductor substrate through the firstinsulating film, forming a second insulating film over an inner wall ofthe trench, filling the trench with a doped polysilicon layer,depositing a third insulating film over the first insulating film, usingthe third insulating film as a mask, removing the first insulating filmto form an opening for defining both a transistor region and a connectregion of the doped polysilicon layer at the same time, forming atransistor on the transistor region, exposing the connect region usingthe third insulating film as the mask, and forming a conductive layer soas to electrically connect one of source and drain regions of thetransistor to the connect region.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel and distinctive features of the invention are set forth in theclaims appended to the present application. The invention itself,however, together with further objects and advantages thereof may bestbe understood by reference to the following description and accompanyingdrawings in which:

FIGS. 1A to 1K are views showing a method of making a semiconductordevice according the first embodiment of the first invention;

FIG. 2A is a view showing a method of making a semiconductor deviceaccording to the first embodiment Of the second invention;

FIG. 2B is a view showing a method of making a semiconductor deviceaccording to the second embodiment of the second invention;

FIGS. 3A and 3B are views showing a method of making a semiconductordevice according to the second embodiment of the first invention;

FIGS. 4A to 4C are views showing a method of making a semiconductordevice according to the first embodiment of the third invention;

FIGS. 5A to 5C are views showing a method of making a semiconductordevice according to the second embodiment of the third invention;

FIGS. 6A and 6B are views showing a conventional method of making asemiconductor device; and

FIG. 7 is a view showing a problem posed in the conventional method ofmaking a semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below with reference to theaccompanying drawings.

FIGS. 1A to 1K are views showing a method of making a substrate platetype DRAM according to the first embodiment of the first invention.

As shown in FIG. 1A, a silicon oxide film (SiO₂ film) 2 and a siliconnitride film (SIN) 3 are formed over a p-type semiconductor substrate 1.After patterning the silicon oxide film 2 and the silicon nitride film3, the patterned silicon nitride film 3 is used as a mask to form atrench 4 in the substrate 1. A silicon oxide film 5 is formed on theinner wall and the bottom surface of the trench 4.

As shown in FIG. 1B, the trench 4 is filled with a n-type dopedpolysilicon layer 6. As shown in FIG. 1C, the patterned silicon nitridefilm 3 is used as a mask to oxidize the surface of the polysilicon layer6, forming a silicon oxide film 7. As shown in FIG. 1D, the 10 siliconnitride film 3 is removed, and a silicon nitride film 8 is then newlyformed over the entire surface.

As shown in FIGS. 1E and 1F, the silicon nitride film 8 is etched tosimultaneously expose the substrate 1 serving as an active region Awhere the MOSFET of a memory cell is formed, and a portion B of theperiphery of the trench 4. Therefore, even if the alignment offset ofthe resist pattern occurs, an interval W between adjacent memory cellsdoes not change (see FIG. 1G). The interval W between the adjacentmemory cells is constantly the same as that when no alignment offset ofthe resist pattern occurs.

As shown in FIG. 1H, the silicon oxide film 2 on the active region A isremoved. As shown in FIG. 1I, a gate insulating film (silicon oxidefilm) 9, a gate electrode 10, and source and drain regions 11 are thenformed on the active region A, thereby completing the MOSFET of thememory cell. A spacer (e.g., a silicon nitride film) 12 and a siliconnitride film 13 are formed on the side wall and the surface of the gateelectrode 10, respectively.

As shown in FIG. 1J, the spacer 12 and the silicon nitride films 8 and13 are used as a mask to etch and remove the silicon oxide film 9(except for a portion serving as the gate insulating film) and part ofthe silicon oxide film 5 on the inner wall of the trench 4, therebyforming a connect region between the capacitor 10 and the MOSFET.

This etching is performed by using the spacer 12 and the silicon nitridefilms 8 and 13 as a mask. For this reason, the connect region betweenthe capacitor and the MOSFET is self-aligned with the element isolationregion and the active region.

As shown in FIG. 1K, a polysilicon film 14 is grown by using a CVDmethod on the source and drain regions 11 and the connect region betweenthe capacitor and the MOSFET. The polysilicon film 14 is etch backedsuch that the polysilicon film 14 is left on only the connect region. Ann-type diffusion layer 15 is formed on part (etched portion) of theinner wall of the trench and the adjacent substrate 1. As a result, thecapacitor constituted by the substrate (electrode) 1, the silicon oxidefilm 5 and the polysilicon layer 6 is connected to the MOSFET.

Finally, the gate electrode 10 of the MOSFET is connected to a word line(not shown), and a bit line and a metal wiring are formed by a knownmethod, thereby completing a DRAM.

According to the above making method, when the silicon nitride film 8 isetched, the substrate 1 serving as the active region A and the portion Bof the periphery of the trench 4 are simultaneously exposed. Therefore,even if the alignment offset of the resist pattern occurs, the intervalW between the adjacent memory cells does not change. The interval W isconstantly the same as that when no alignment offset of the resistpattern occurs. That is, the interval between the n-type diffusion layer15 of a memory cell and the source and drain regions of the adjacentmemory cell does not decrease even if the alignment offset of the resistpattern occurs.

FIG. 2A is a view showing a method of making a semiconductor deviceaccording to the first embodiment of the second invention. The presentinvention relates to a method of combining semiconductor layers eachother.

An insulating film 22 is formed on a p-type substrate 21, and openingsare formed in part of the insulating film 22. By using a selectiveepitaxy growth method (to be referred to as the SEG method hereinafter),a semiconductor layer 23A is then grown from one opening, and asemiconductor layer 23B is grown from another opening. The semiconductorlayer 23A grown from one opening by using the p-type substrate 21 as anucleus is combined with the semiconductor layer 23B grown from anotheropening by using the p-type substrate 21 as a nucleus.

According to the above making method, the semiconductor layers can beeasily connected to each other. Although, in the above embodiment, thep-type semiconductor substrate 21 is used, an n-type semiconductorsubstrate may also be used.

FIG. 2B is a view showing a method of making a semiconductor deviceaccording to the second embodiment of the second invention.

A trench 24 is formed in a p-type substrate 21, and an insulating film25 is formed on the inner wall and the bottom surface of the trench 24.The trench 24 is filled with an n-type polysilicon film 26. By using theSEG method, a semiconductor layer 27A is grown from the p-type substrate21 and a semiconductor layer 27B is grown from the n-type polysiliconlayer 26. The semiconductor layer 27A grown by using the p-typesubstrate 21 as a nucleus is combined with the semiconductor layer 27Bgrown by using the n-type polysilicon layer 26 as a nucleus.

According to the above making method, the semiconductor layer of thefirst conductivity type can be easily connected with the semiconductorlayer of the second conductivity type.

The second invention can be applied to the first invention. Morespecifically, in the first embodiment of the first invention, the SEGmethod can be used when the source and drain regions 11, the capacitorof the MOSFET are connected.

FIGS. 3A and 3B are views showing a method of making a substrate platetype DRAM according to the second embodiment of the first invention.

By using the same method as in the first embodiment of the firstinvention, the MOSFET of a memory cell, which is constituted by a gateinsulating film 9, a gate electrode 10, and source and drain regions 11,is formed on an active region A. A spacer 12 and a silicon nitride film13 are formed on the side wall and the surface of the gate electrode 10,respectively (see FIGS. 1A to 1I).

As shown in FIG. 3A, the spacer 12 and silicon nitride films 8 and 13are used as a mask to etch and remove the silicon oxide film 9 (exceptfor a portion serving as the gate insulating film), and part of siliconoxide films 5 and 7 on the trench 4, thereby forming a connect regionbetween the capacitor and the MOSFET. This embodiment differs from thefirst embodiment of the first invention in that the silicon oxide film 5on the inner wall of the trench 4 is not etched.

This etching is performed by using the spacer 12 and the silicon nitridefilms 8 and 13 as a mask. For this reason, the connect region betweenthe capacitor and the MOSFET is self-aligned with the element isolationregion and the active region.

As shown in FIG. 3B, a semiconductor film 14 is formed on the source anddrain regions 11 and the connect region between the capacitor and theMOSFET. As a result, the capacitor constituted by the substrate(electrode) 1, the silicon oxide film 5, and the polysilicon layer 6 isconnected to the MOSFET.

Finally, the gate electrode 10 of the MOSFET is connected to a wordline, and a bit line and a metal wiring are formed by a known method,thereby completing a DRAM.

Also in the above making method, the same effect as in the firstembodiment of the first invention can be obtained.

FIGS. 4A to 4C are views showing a method of making a substrate platetype DRAM according to the first embodiment of the third invention.

By the same method as in the first embodiment of the first invention, asilicon nitride film 8 is etched to simultaneously expose a substrate 1serving as an active region A and a portion B of the periphery of atrench 4 (see FIGS. 1A to 1G).

As in the first embodiment, in exposure of the active region A and theportion B of the periphery of the trench 4, an interval w betweenadjacent memory cells does not change even if the alignment offset ofthe resist pattern occurs. The interval W between the adjacent memorycells is constantly the same as that when no alignment of the resistpatter occurs.

As shown in FIG. 4A, the silicon nitride film 8 is used as a mask toetch and remove a silicon oxide film 2 on the active region A, part of asilicon oxide film 7 on the trench, and part of a silicon oxide film 5on the inner wall of the trench.

As shown in FIG. 4B, by using the SEG method, a single-crystal siliconfilm 14A is grown on the substrate (active region) 1, and a polysiliconfilm 14B is grown on the trench (connect region between the capacitorand the MOSFET). The single-crystal silicon film 14A is combined withthe polysilicon film 14B.

Annealing is then performed to diffuse an n-type impurity contained in apolysilicon layer 6 in the trench into the substrate or the siliconfilms 14A and 14B at the peripheral portion of the trench. As a result,an n-type diffusion layer 15 is formed in the substrate 1. A capacitoris constituted by the substrate 1, the silicon oxide film 5, and thepolysilicon layer 6.

As shown in FIG. 4C, a gate insulating film (silicon oxide film) 9, agate electrode 10, and source and drain regions 11 are formed on thesingle-crystal silicon film 14A, thereby completing the MOSFET of amemory cell. A spacer (e.g., silicon nitride film) 12 and a siliconnitride film 13 are formed on the side wall and the surface of the gateelectrode 10, respectively.

Finally, the gate electrode 10 of the MOSFET is connected to a word line(not shown), and a bit line and a metal wiring are formed by a knownmethod, thereby completing a DRAM.

Also in the above making method, when the silicon nitride film 8 isetched, the substrate 1 serving as the active region A where the MOSFETof the memory cell is formed, and the portion B of the periphery of thetrench 4 are simultaneously exposed. Therefore, even if the alignmentoffset of the resist pattern occurs, an interval W between adjacentmemory cells does not change. The interval W is constantly the same asthat when no alignment offset of the resist pattern occurs. That is, theinterval between the n-type diffusion layer 15 of a memory cell and thesource and drain regions of the adjacent memory cell does not decreaseeven if the alignment offset of the resist pattern occurs.

In this embodiment, the single-crystal silicon film 14A and thepolysilicon film 14B are grown by the SEG method on the substrate(active region) 1 and the trench (connect region between the capacitorand the MOSFET), respectively, and the single-crystal silicon film 14Ais combined with the polysilicon film 14B. Therefore, the MOSFET and thecapacitor can be easily connected to each other.

FIGS. 5A to 5C are views showing a method of making a substrate platetype DRAM according to the second embodiment of the third invention.

By the same method as in the first embodiment of the first invention, asilicon nitride film 8 is etched to simultaneously exposure a substrate1 serving as an active region A where the MOSFET of a memory cell isformed, and a portion B of the periphery of a trench 4 (see FIGS. 1A to1G).

As in the first embodiment, in exposure of the active region A and theportion B of the periphery of the trench 4, even if the alignment offsetof the resist pattern occurs, an interval W between adjacent memorycells does not change. The interval W between the adjacent memory cellsis constantly the same as that when no alignment offset of the resistpattern occurs.

As shown in FIG. 5A, the silicon nitride film 8 is used as a mask toetch and remove a silicon oxide film 2 on the active region A and partof a silicon oxide film 7 on the trench. This embodiment differs fromthe first embodiment of the third invention in that a silicon oxide film5 on the inner wall of the trench is not etched and removed.

As shown in FIG. 5B, by using the SEG method, a single-crystal siliconfilm 14A is grown on the substrate (active region) 1, and a polysiliconfilm 14B is grown on the trench (connect region between the capacitorand the MOSFET). The single-crystal silicon film 14A is combined withthe polysilicon film 14B.

Annealing is then performed to diffuse an n-type impurity contained in apolysilicon layer 6 in the trench into the silicon films 14A and 14B onthe trench. As a result, an n-type diffusion layer 15 is formed in 10the silicon films 14A and 14B on the trench. A capacitor is constitutedby the substrate 1, the silicon oxide film 5, and the polysilicon layer6.

As shown in FIG. 5C, a gate insulating film (silicon oxide film) 9, agate electrode 10, and source and drain regions 11 are formed on thesingle-crystal silicon film 14A, thereby completing the MOSFET of amemory cell. A spacer (e.g., silicon nitride film) 12 and a siliconnitride film 13 are formed on the side wall and the surface of the gateelectrode 10, respectively.

Finally, the gate electrode 10 of the MOSFET is connected to a word line(not shown), and a bit line and a metal wiring are formed by a knownmethod, thereby completing a DRAM.

Also in the above method, the same effect as in the first embodiment ofthe third invention can be obtained.

In the first and third inventions, the substrate plate type DRAM hasbeen exemplified. However, the present invention is not limited to this.For example, the present invention can be applied to a semiconductordevice such as a stack trench or sheath plate type DRAM, in which anopening for connecting the MOSFET is formed in the inner wall portion ofthe trench where the capacitor is formed.

It is further understood by those skilled in the art that the foregoingdescription is only of the preferred embodiments and that variouschanges and modifications may be made in the invention without departingfrom the spirit and scope thereof.

What is claimed is:
 1. A method of making a semiconductor memory devicecomprising the step of:(a) preparing a semiconductor substrate of afirst conductivity type; (b) forming a first insulating film over saidsemiconductor substrate; (c) forming a trench in said semiconductorsubstrate through said first insulating film; p1 (d) forming a secondinsulating film over an inner wall of said trench; (e) filling saidtrench with a doped polysilicon layer; (f) depositing a third insulatingfilm over said first insulating film; (g) using said third insulatingfilm as a mask, removing said first insulating film to form an openingfor defining both a transistor region and a connect region of said dopedpolysilicon layer at the same time; (h) forming a transistor on saidtransistor region; (i) exposing said connect region using said thirdinsulating film as said mask; and (j) forming a conductive layer so asto electrically connect one of source and drain regions of saidtransistor to said connect region.
 2. The method according to claim 1,wherein said first insulating layer is silicon oxide, and said thirdinsulating layer is silicon nitride.
 3. The method according to claim 1,wherein said active region is continuous to said connect region.
 4. Amethod of making a semiconductor memory device comprising the stepof:(a) preparing a semiconductor substrate of a first conductivity type;(b) forming a first insulating film over said semiconductor substrate;(c) forming a trench in said semiconductor substrate through said firstinsulating film; (d) forming a second insulating film over an inner wallof said trench; (e) filling said trench with a doped polysilicon layer;(f) depositing a third insulating film over said first insulating film;(g) using said third insulating film as a mask, removing said firstinsulating film from said semiconductor substrate so as to expose a partof said doped polysilicon layer; (h) growing a semiconductor layer onsaid semiconductor substrate to provide a polycrystalline semiconductorlayer on the exposed portion of said doped polysilicon layer; and (i)forming a transistor on said semiconductor layer.
 5. The methodaccording to claim 4, wherein the step (f) defines a connect region forelectrically connecting one of source and drain regions of saidtransistor to said doped polysilicon layer.